Multilayer printed circuit boards (PCB's) are typically constructed by interleaving imaged conductive layers such as one containing copper with non-conductive layers such as a partially cured B-stage resin, i.e., a prepreg, into a multilayer sandwich which is then bonded together by applying heat and pressure. The conductive layer, e.g., copper circuitry, does not bond well to the non-conductive B-stage resin prepreg. Often intermediate layers are used to bond the B-stage prepreg to the copper circuitry.
In the formation of multilayer circuit boards, it is often necessary to drill holes through the boards, and defects can occur due to delamination of layers in the areas immediately surrounding a hole. Additionally, hole cleaning chemicals (typically acidic or reductive) can remove the bonding metal oxide-metal hydroxide layer. This removal leads to partial delamination, known as pink ring. When the multilayer structures are exposed to elevated temperatures for extended periods of time, decay of the bond strength may occur. It is desirable to have materials which can be used to prepare multilayer structures without the above problems.
U.S. Pat. No. 4,499,152, issued to Green et al, relates to metal-clad laminate construction. The laminate is useful in high resolution printed circuit patterns. The laminate preferably comprises a resin-bonded, glass-reinforced substrate, a layer of coupling agent covering and bonded to the major surface of the substrate, a layer of ultra-thin copper adjacent the layer of coupling agent, and a composite bonding layer disposed between the copper layer and the layer of coupling agent. The composite bonding layer comprises copper alloy with at least one non-copper metal and oxide material of non-copper metal. The aluminum sheet carrier material is covered with a thin film of copper by vapor deposition. The thin film of copper is then coated with a thin layer of a metal oxide or mixture of metal oxides.
U.S. Pat. No. 4,882,202, issued to Holtzman et al, relates to the use of immersion tin and tin alloys as bonding media for multilayer circuits. Holtzman et al disclose a method for improving the adhesion of printed circuit boards to one another in a multilayer board using an immersion tin composition containing urea compounds.
U.S. Pat. No. 5,073,456, issued to Palladino, relates to multilayer printed circuit board. The multilayer printed circuit boards, having a number of through-holes, are prepared by forming an electrically conductive copper circuitry on the surface of a dielectric material and forming a layer of oxide, hydroxide or combinations thereof of tin on the copper circuitry, applying a silane bonding mixture to the surface of the metal oxide, metal hydroxide or combination thereof layer or to an insulating layer to be bonded to the copper circuitry, wherein the insulating layer comprises a partially cured thermosetting polymer composition and the silane bonding mixture consists essentially of a ureido silane and a disylyl crosslinking agent. A number of through holes are formed in the bonded article and the walls of the through holes are metalized to form electrically conductive paths.